package com.xaicode.algorithm.leetcode._1_100;

/**
 * <a href="https://leetcode-cn.com/problems/add-two-numbers">两数相加</a>
 *
 * <p>给你两个 <strong>非空</strong> 的链表，表示两个非负的整数。
 * 它们每位数字都是按照 <strong>逆序</strong> 的方式存储的，
 * 并且每个节点只能存储 <strong>一位</strong> 数字。</p>
 *
 * <p>请你将两个数相加，并以相同形式返回一个表示和的链表。</p>
 *
 * <p>你可以假设除了数字 0 之外，这两个数都不会以 0 开头。</p>
 *
 * <p> </p>
 *
 * <p><strong>示例 1：</strong></p>
 * <img alt="" src="https://cdn.jsdelivr.net/gh/doocs/leetcode@main/solution/0000-0099/0002.Add%20Two%20Numbers/images/addtwonumber1.jpg" style="width: 483px; height: 342px;" />
 * <pre>
 * <strong>输入：</strong>l1 = [2,4,3], l2 = [5,6,4]
 * <strong>输出：</strong>[7,0,8]
 * <strong>解释：</strong>342 + 465 = 807.
 * </pre>
 *
 * <p><strong>示例 2：</strong></p>
 *
 * <pre>
 * <strong>输入：</strong>l1 = [0], l2 = [0]
 * <strong>输出：</strong>[0]
 * </pre>
 *
 * <p><strong>示例 3：</strong></p>
 *
 * <pre>
 * <strong>输入：</strong>l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
 * <strong>输出：</strong>[8,9,9,9,0,0,0,1]
 * </pre>
 *
 * <p> </p>
 *
 * <p><strong>提示：</strong></p>
 *
 * <ul>
 * 	<li>每个链表中的节点数在范围 <code>[1, 100]</code> 内</li>
 * 	<li><code>0 <= Node.val <= 9</code></li>
 * 	<li>题目数据保证列表表示的数字不含前导零</li>
 * </ul>
 *
 * @author beborn xaicode@sina.com
 */
public class _2_Middle_AddTwoNumbers {

    public static void main(String[] args) {

    }

    public ListNode addTwoNumbers1(ListNode l1, ListNode l2) {
        ListNode head = null, tail = null;
        int carry = 0;
        while (l1 != null || l2 != null) {
            int n1 = l1 != null ? l1.val : 0;
            int n2 = l2 != null ? l2.val : 0;
            int sum = n1 + n2 + carry;
            if (head == null) {
                head = tail = new ListNode(sum % 10);
            } else {
                tail.next = new ListNode(sum % 10);
                tail = tail.next;
            }
            carry = sum / 10;
            if (l1 != null) {
                l1 = l1.next;
            }
            if (l2 != null) {
                l2 = l2.next;
            }
        }
        if (carry > 0) {
            tail.next = new ListNode(carry);
        }
        return head;
    }

    public ListNode addTwoNumbers2(ListNode l1, ListNode l2) {
        // simulation stack with head 0
        ListNode head = new ListNode(0);
        ListNode tail = head;
        int carry = 0;
        while (l1 != null || l2 != null || carry != 0) {
            int sum = (l1 == null ? 0 : l1.val) + (l2 == null ? 0 : l2.val) + carry;
            carry = sum / 10;
            tail.next = new ListNode(sum % 10);
            tail = tail.next;
            l1 = l1 == null ? null : l1.next;
            l2 = l2 == null ? null : l2.next;
        }
        return head.next;
    }


    /**
     * simulation stack
     */
    public static class ListNode {
        int val;
        ListNode next;

        ListNode() {
        }

        ListNode(int val) {
            this.val = val;
        }

        ListNode(int val, ListNode next) {
            this.val = val;
            this.next = next;
        }
    }

}
